1. Geology

2. A Layered Earth
No physical samples from beneath outermost layer of earth!!!!
Clues from:
Heat measurements leaking from interior
Chemical composition of volcanic gases
Chemical composition of volcanic rock
Studies of shocks from distant earthquakes
Seismic waves

4. Lithosphere
Cool, rigid, ~60 miles thick
Asthenosphere
Thin, hot flowing ~430 miles thick

5. A New Age In Geology

6. Continental Drift Puzzle like fit of continents
Even better fit of continental shelves
Same fossils on 2 coastlines
Coal in Antarctica
1912 Wegener - continental drift
Original Land Mass - Pangaea

10. 20th Century Additions to Theory:
Earthquakes/volcanoes not random

11. Dating of seafloor = 200 MYO
Continents BYO
Seismic studies suggest molten layer
Discovery of Mid Atlantic Ridge

12. Sea Floor Spreading If new material is being formed it should be hot
It is
The farther away from the ridge the rock should be younger
As it cools and shrinks as it moves away from ridge, it should shrink and increase density
It does
Sediments should be thicker at edges of oceans than in the middle
They are

13. As earth’s magnetic poles reverse, there should be stripes of rock with minerals pointing to where north was at the time.
There is

14. Plate Tectonics
A new name for the 2 old theories - continental drift and seafloor spreading combined
Slow!!!!! 2 inches/year in Atlantic
4.8 cubic miles of new seafloor each year

16. Types of Plate margins 1) Convergent Plates moving together
When both rise - mountains
When one subducts another - volcanoes

17. 2) Divergent When plates move apart Creates shallow volcanoes
mid Atlantic rift and Iceland great examples of this

18. 3) Transform When plates are rubbing side by side
Pressure builds and they can ‘lurch”
Causes earthquakes
San Andreas fault